As we have seen the Lightning Network uses a sourced base Onion Routing Protocol to deliver a payment from a sender to the recipient. For this the sending node has to be able to construct a path of payment channels that connects it with the recipient. Thus the sender has to be aware of the Channel Graph. The channel graph is the interconnected set of publicly advertised channels (more on that later), and the nodes that these channels interlink. As channels are backed by a funding transaction that is happening on chain one might falsely believe that Lightning Nodes could just extract the existing channels from the Bitcoin Blockchain. However this only possible to a certain extend. The Funding transactions are Pay to Whitness Script addresses and the nature of the script will only be revealed once the funding transaction output is spent. Even if the nature of the script was known we emphasize that not all 2 - of - 2 multisignature scripts correspond to payment channels. Since not even every Pay to Whitness Script address that we see in the Bitcoin Blockchain corresponds to a payment channel this approach is not helpful. There are actually more reasons why looking at the Bitcoin Blockchain might not be helpful. For example on the Lightnign Network the Bitcoin keys that are used for signing are rotated by the nodes for every channel and update. Thus even if we could reliably detect funding transactions on the Bitcoin Blockchain we would not know which two nodes on the Lightning Network own that particular channel. Thus we could node create the Channel Graph that would be used to create candidate paths during the payment delivery via onion routing.
The Lightning Network solves the afore mentioned problem by implementing a gossip protocol. Gossip protocols are typical for peer 2 peer networks and are being used so that nodes can share information with other nodes without talking to those other nodes directly. For that Lightning Nodes open encrypted peer 2 peer connections to each other and share novel information that they have received from other peers. As soon as a node wants to share some information - for example about a newly created channel - it sends a message to all its peers. Uppon receiving a message a node decides if the received message was novel and if so it will forward the information to its peers. In this way if the peer 2 peer network is connected all new information that is necessary for the operation of the network will eventually be propagated to all other peers.
Obviously if a new peer initially wants to join the network it needs to know some other peers on the Network initially. Only then the new peer could connect to them in order to learn about the existance of other peers. In this chapter, we’ll explore exactly how Lightning nodes discover each other, and also the channel graph itself. When most refer to the network part of the Lightning Network, they’re referring to the Channel Graph which itself is a unique authenticated data structure anchored in the base Bitcoin blockchain. However the Lightning network is also a peer to peer network of nodes that are have just opened an encrypted peer connection. Usually for 2 peers to maintain a payment channel they need to talk to each other directly which means that there will be a peer connection between them. This suggests that the Channel Graph is a subnetwork of the peer to peer network. However this is not true. As payment channels do not need to be closed if one or both peers are going offline they can continue to exist even though the peer connection is terminated. It might be usefull to get familiar with the different terminology that we have used througout the book for similar concepts / actions depending on weather they happen on the Channel Graph or on the peer 2 peer network.
| Channel Graph | peer to peer network | |
|---|---|---|
Name |
channel |
connection |
initiate |
open |
(re)connect |
finalize |
close |
terminate |
technology |
Bitcoin Blockchain |
encrypted TCP/IP connection |
lifetime |
until funding spent |
while peers are online |
As the Lightning Network is a peer-to-peer network, some initial bootstrapping is required in order for peers to discover each other. Within this chapter we’ll follow the story of a new peer connecting to the network for the first time, and examine each step in the bootstrapping process from initial peer discovery, to channel graph syncing and validation.
As an initial step, our new node needs to somehow discover at least one peer that is already connected to the network and has a full channel graph (as we’ll see later, there’s no canonical version as the update dissemination system is eventually consistent). Using one of many initial bootstrapping protocols to find that first peer, after a connection is established, our new peer now needs to download and validate the channel graph. Once the channel graph has been fully validated, our new peer is ready to start opening channels and sending payments on the network.
After initial bootstrap, a node on the network needs to continue to maintain its view of the channel graph by: processing new channel routing policy updates, discovering and validating new channels, removing channels that have been closed on chain, and finally pruning channels that fail to send out a proper "heartbeat" every 2 weeks or so.
Upon completion of this chapter, the reader will understand a key component of the p2p Lightning Network: namely how peers discover each other and maintain a personal view of the channel graph. We’ll being our story with exploring the story of a new node that has just booted up, and needs to find other peers to connect to on the network.
In this section, we’ll begin to follow the story of Norman, a new Lightning node that wishes to join the network as he sets out on his journey to which consists of 3 steps:
-
discovery a set of bootstrap peers.
-
download and validate the channel graph.
-
begin the process of ongoing maintainance of the channel graph itself.
Before doing any thing else, Norman first needs to discover a set of peers whom are already part of the network. We call this process initial peer bootstrapping, and it’s something hat every peer to peer network needs to implement properly in order to ensure a robust, healthy network. Bootstrapping new peers to existing peer to peer networks is a very well studied problem with several known solutions, each with their own distinct trade offs. The simplest solution to this problem is simply to package a set of hard coded bootstrap peers into the packaged p2p node software. This is simple in that each new node can find the bootstrap peer with nothing else but the software they’re running, but rather fragile given that if the set of bootstrap peers goes offline, then no new nodes will be able to join the network. Due to this fragility, this option is usually used as a fallback in case none of the other p2p bootstrapping mechanisms work properly.
Rather than hard coding the set of bootstrap peers within the software/binary itself, we can instead opt to devise a method that allows peers to dynamically obtain a fresh/new set of bootstrap peers they can use to join the network. We’ll call this process initial peer discovery. Typically we’ll leverage existing Internet protocols to maintain and distribute a set of bootstrapping peers. A non-exhaustive list of protocols that have been used in the past to accomplish initial peer discovery include:
-
DNS
-
IRC
-
HTTP
Similar to the Bitcoin protocol, the primary initial peer discovery mechanism used in the Lightning Network happens via DNS. As initial peer discovery is a critical and universal task for the network, the process has been standardized in a document that is a part of the Basis of Lightning Technology (BOLT) specification. This document is [BOLT 10](https://github.com/lightningnetwork/lightning-rfc/blob/master/10-dns-bootstrap.md).
The BOLT 10 document describes a standardized way of implementing peer discovery using the Domain Name System (DNS). Lightning’s flavor of DNS based bootstrapping uses up to 3 distinct record types:
-
SRVrecords for discovering a set of node public keys. -
Arecords for mapping a node’s public key to its currentIPv4address. -
AAArecords for mapping a node’s public key to its currentIPv6address (if one exists).
Those somewhat familiar with the DNS protocol may already be familiar with the
A and AAA record types, but not the SRV type. The SRV record type is
used less commonly by protocols built on DNS, that’s used to determine the
location for a specified service. In our context, the service in question is
a given Lightning node, and the location its IP address. We need to use this
additional record type as unlike nodes within the Bitcoin protocol, we need
both a public key and an IP address in order to connect to a node. As we saw
in chapter XX on the transport encryption protocol used in LN, by requiring
knowledge of the public key of a node before one can connect to it, we’re able
to implement a form of identity hiding for nodes in the network.
Before diving into the specifics of BOLT 10, we’ll first outline the high level flow of a new node that wishes to use BOLT 10 to join the network.
First, a node needs to identify a single, or set of DNS servers that understand BOLT 10 so they can be used for p2p bootstrapping. While BOLT 10 uses lseed.bitcoinstats.com as the seed server as the example there exists no "official" set of DNS seeds for this purpose, but each of the major implementations maintain their own DNS seed, and cross query each other’s seeds for redundancy purposes.
[[dns seeds]] .Table of known lightning dns seed servers
| dns server | Maintainer |
|---|---|
lseed.bitcoinstats.com |
Christian Decker |
nodes.lightning.directory |
lightning labs (Olaoluwa Osuntokun) |
soa.nodes.lightning.directory |
lightning labs (Olaoluwa Osuntokun) |
lseed.darosior.ninja |
Antoine Poinsot |
DNS seeds exist for both Bitcoin’s mainnet and testnet. For the sake
of our example, we’ll assume the existence of a valid BOLT 10 DNS seed at
nodes.lightning.directory.
Next, we’ll now issue an SRV query to obtain a set of candidate bootstrap
peers. The response to our query will be a series of bech32 encoded public
keys. As DNS is a text based protocol, we can’t send raw bytes, so an encoding
scheme is required. For this scheme BOLT 10 has selected bech32 due to its
existing propagation in the wider Bitcoin ecosystem. The number of encoded
public keys returned depends on the server returning the query, as well as all
the resolver that stand between the client and the authoritative server. Many
resolvers may filter out SRV records all together, or attempt to truncate the
response size itself.
Using the widely available dig command-line tool, we can query the testnet
version of the DNS seed mentioned above with the following command:
$ dig @8.8.8.8 test.nodes.lightning.directory SRVWe use the @ argument to force resolution via Google’s nameserver as they
permit our larger SRV query responses. At the end, we specify that we only want
SRV records to be returned. A sample response looks something like:
$ dig @8.8.8.8 test.nodes.lightning.directory SRV
; <<>> DiG 9.10.6 <<>> @8.8.8.8 test.nodes.lightning.directory SRV
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 43610
;; flags: qr rd ra; QUERY: 1, ANSWER: 25, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;test.nodes.lightning.directory. IN SRV
;; ANSWER SECTION:
test.nodes.lightning.directory. 59 IN SRV 10 10 9735 ln1qfkxfad87fxx7lcwr4hvsalj8vhkwta539nuy4zlyf7hqcmrjh40xx5frs7.test.nodes.lightning.directory.
test.nodes.lightning.directory. 59 IN SRV 10 10 15735 ln1qtgsl3efj8verd4z27k44xu0a59kncvsarxatahm334exgnuvwhnz8dkhx8.test.nodes.lightning.directory.
<SNIP>
;; Query time: 89 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Thu Dec 31 16:41:07 PST 2020We’ve truncated the response for brevity. In our truncated responses, we can
see two responses. Starting from the right-most column, we have a candidate
"virtual" domain name for a target node, then to the left we have the port
that this node can be reached using. The first response uses the standard port
for LN: 9735. The second response uses a custom port which is permitted by
the protocol.
Next, we’ll attempt to obtain the other piece of information we need to connect to a node: it’s IP address. Before we can query for this however, we’ll fist decode the returned sub-domain for this virtual host name returned by the server. To do that, we’ll first encoded public key:
ln1qfkxfad87fxx7lcwr4hvsalj8vhkwta539nuy4zlyf7hqcmrjh40xx5frs7Using bech32, we can decode this public key to obtain the following valid
secp256k1 public key:
026c64f5a7f24c6f7f0e1d6ec877f23b2f672fb48967c2545f227d70636395eaf3Now that we have the raw public key, we’ll now ask the DNS server to resolve the virtual host given so we can obtain the IP information for the node:
$ dig ln1qfkxfad87fxx7lcwr4hvsalj8vhkwta539nuy4zlyf7hqcmrjh40xx5frs7.test.nodes.lightning.directory A
; <<>> DiG 9.10.6 <<>> ln1qfkxfad87fxx7lcwr4hvsalj8vhkwta539nuy4zlyf7hqcmrjh40xx5frs7.test.nodes.lightning.directory A
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 41934
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;ln1qfkxfad87fxx7lcwr4hvsalj8vhkwta539nuy4zlyf7hqcmrjh40xx5frs7.test.nodes.lightning.directory. IN A
;; ANSWER SECTION:
ln1qfkxfad87fxx7lcwr4hvsalj8vhkwta539nuy4zlyf7hqcmrjh40xx5frs7.test.nodes.lightning.directory. 60 IN A X.X.X.X
;; Query time: 83 msec
;; SERVER: 2600:1700:6971:6dd0::1#53(2600:1700:6971:6dd0::1)
;; WHEN: Thu Dec 31 16:59:22 PST 2020
;; MSG SIZE rcvd: 138In the above command, we’ve queried the server so we can obtain an IPv4
address for our target node. Now that we have both the raw public key and IP
address, we can connect to the node using the brontide transport protocol at:
026c64f5a7f24c6f7f0e1d6ec877f23b2f672fb48967c2545f227d70636395eaf3@X.X.X.X.
Querying for the curent A record for a given node can also be used to look up
the latest set of addresses for a given node. Such queries can be used to
more quickly (compared to waiting on gossip as we’ll cover later) sync the
latest addressing information for a node.
At this point in our journey, Norman our new Lightning Node has found its first peer and established its first connect! Now we can being the second phase of new peer bootstrapping: channel graph synchronization and validation, but first, we’ll explore more of the intricacies of BOLT 10 itself to take a deeper look into how things work under the hood.
As we learned earlier in the chapter, BOLT 10 describes the standardized protocol for boostrapping new peer suing the DNS protocol. In this section, we’ll dive into the details of BOLT 10 itself in order to explore exactly how bootstrapping queries are made, and also the additional set of options available for querying.
The BOLT 10 standard is highly extensible due to its usage of nested sub-domains as a communication layer for additional query options. The bootstrapping protocol allows clients to further specify the type of nodes they’re attempting to query for vs the default of receiving a random subset of nodes in the query responses.
The query option sub-domain scheme uses a series of key-value pairs where the key itself is a single letter and the remaining set of text is the value itself. The following query types exist in the current version of the BOLT 10 standards document:
-
r: The "realm" byte which is used to determine which chain or realm queries should be returned for. As is, the only value for this key is0which denotes Bitcoin itself. -
a: Allows clients to filter out returned nodes based on the types of addresses they advertise. As an example, this can be used to only obtain nodes that advertise a valid IPv6 address. -
The value that follows this type is based on a bitfled that indexes into the set of specified address type which are defined in BOLT 7. We’ll cover this material shortly later in this chapter once we examine the structure of the channel graph itself.
-
The default value for this field is
6, which is2 || 4, which denotes bit 1 and 2, which are IPv4 and IPv6. -
l: A valid node public key serialized in compressed format. This allows a client to query for a specified node rather than receiving a set of random nodes. -
n: The number of records to return. The default value for this field is25.
An example query with additional query options looks something like the following:
r0.a2.n10.nodes.lightning.directoryBreaking down the query one key-value pair at a time we gain the following insights:
-
r0: The query targets the Bitcoin realm. -
a2: The query only wants IPv4 addresses to be returned. -
n10: The query requests
Now that Norman is able to use the DNS boostrapping protocol to connect to his very first peer, we can now start to sync the channel graph! However, before we sync the channel graph, we’ll need to learn exactly what we mean by the channel graph. In this section we’ll explore the precise structure of the channel graph and examine the unique aspects of the channel graph compared to the typical abstract "graph" data structure which is well known/used in the field of Computer Science.
A graph in computer science is a special data structure composed of vertices (typically referred to as nodes) and edges (also known as links). Two nodes may be connected by one or more edges. The channel graph is also directed given that a payment is able to flow in either direction over a given edge (a channel). As we’re concerned with routing payments, in our model a node with no edges isn’t considered to be a part of the graph as it isn’t "productive". In the context of the Lightning Network, our vertices are the Lightning nodes themselves, with our edges being the channels that connect these nodes. As channels are themselves a special type of multi-sig UTXO anchored in the base Bitcoin blockchain, possible to scan the chain (with the assistance of special meta data proofs) and re-derive the channel graph first-hand (though we’d be missing some information as we see below).
As channels themselves are UTXOs, we can view the channel graph as a special sub-set of the UTXO set, on top of which we can add some additional information (the nodes, etc) to arrive at the final overlay structure which is the channel graph. This anchoring of fundamental components of the cahnnel graph in the base Bitcoin blockchain means that it’s impossible to fake a valid channel graph, which has useful properties when it comes to spam prevention as we’ll see later. The channel graph in the Lightning Network is composed of 3 individual components which are described in BOLT 7:
-
node_announcement: The vertex in our graph which communicates the public key of a node, as well as how to reach the node over the internet and some additional metadata describing the set of features the node supports. -
channel_announcement: A blockchain anchored proof of the existence of a channel between two individual nodes. Any 3rd party can verify this proof in order to ensure that a real channel is actually being advertised. Similar to thenode_announcementthis message also contains information describing the capabilities of the channel which is useful when attempting to route a payment. -
channel_update: A pair of structures that describes the set of routing policies for a given channel. `channel_update`s come in a pair as a channel is a directed edge, so both sides of the channel are able to specify their own custom routing policy. An example of a policy communicated in a
It’s important to note that each of components of the channel graph are
themselves authenticated allowing a 3rd party to ensure that the owner of a
channel/update/node is actually the one sending out an update. This effectively
makes the Channel Graph a unique type of authenticated data structure that
cannot be counterfeited. For authentication, we use an secp256k1 ECDSA
digital signature (or a series of them) over the serialized digest of the
message itself. We won’t get into the specific of the messaging
framing/serialization used in the LN in this chapter, as we’ll cover that
information in Chapter XX on the wire protocol used in in the protocol.
With the high level structure of the channel graph laid out, we’ll now dive down into the precise structure of each of the 3 components of the channel graph. We’ll also explain how one can also verify each component of the channel graph as well.
First, we have the node_announcement which plays the role of the vertex in
the channel graph. A node’s announcement in the network serves to primary
purposes:
-
To advertise connection information so other nodes can connect to it, either to bootstrap to the network, or to attempt to establish a set of new channels.
-
To communicate the set of features protocol level features a node understands. This communication is critical to the decentralized de-synchronized update nature of the Lightning Network itself.
Unlike channel announcements, node announcements aren’t actually anchored in the base blockchain. As a result, advertising a node announcement in isolation bares no up front cost. As a result, we require that all node announcements are only considered "valid" if it has propagated with a corresponding channel announcement as well. In other words, we always reject unconnected nodes in order to ensure a rogue peer can’t fill up our disk with bogus nodes that may not actually be part of the network.
The node announcement is a simple data structure that needs to exist for each node that’s a part of the channel graph. The node announcement is comprised of the following fields, which are encoded using the wire protocol structure described in BOLT 1:
-
signature: A valid ECDSA signature that covers the serialized digest of all fields listed below. This signature MUST be venerated by the private key that backs the public key of the advertised node. -
features: A bit vector that describes the set of protocol features that this node understands. We’ll cover this field in more detail in Chapter XX on the extensibility of the Lightning Protocol. At a high level, this field carries a set of bits (assigned in pairs) that describes which new features a node understands. As an example, a node may signal that it understands the latest and greatest channel type, which allows peers that which bootstrap to the network to filter out the set of nodes they want to connect to. -
timestamp: A timestamp which should be interpreted as a unix epoch formatted timestamp. This allows clients to enforce a partial ordering over the updates to a node’s announcement. -
node_id: Thesecp256k1public key that this node announcement belongs to. There can only be a singlenode_announcementfor a given node in the channel graph at any given time. As a result, anode_announcementcan superseded a priornode_announcementfor the same node if it carries a higher time stamp. -
rgb_color: A mostly unused field that allows a node to specify an RGB "color" to be associated with it. -
alias: A UTF-8 string to serve as the nickname for a given node. Note that these aliases aren’t required to be globally unique, nor are they verified in any shape or form. As a result, they are always to be interpreted as being "unofficial". -
addresses: A set of public internet reachable addresses that are to be associated with a given node. In the current version of the protocol 4 address types are supported: IPv4 (1), IPv6 (2), Tor V2 (3), Tor V3 (4). On the wire, each of these address types are denoted by an integer type which is included in parenthesis after the address type.
Validating an incoming node_announcement is straight forward, the following
assertions should be upheld when examining a node announcement:
-
If an existing
node_announcementfor that node is already known, then thetimestampfield of a new incomingnode_announcementMUST be greater than the prior one. -
With this constraint, we enforce a forced level of "freshness".
-
If no
node_announcementexist for the given node, then an existingchannel_announcementthat refernces the given node (more on that later) MUST already exist in one’s local channel graph. -
The included
signatureMUST be a valid ECDSA signature verified using the includednode_idpublic key and the double-sha256 digest of the raw message encoding (mins the signature and frame header!) as the message. -
All included
addressesMUST be sorted in ascending order based on their address identifier. -
The included
aliasbytes MUST be a valid UTF-8 string.
Next, we have the channel_announcement. This message is used to announce a
new public channel to the wider network. Note that announcing a channel is
optional. A channel only needs to be announced if its intended to be used for
routing by the public network. Active routing nodes may wish to announce all
their channels. However, certain nodes like mobile nodes likely don’t have the
uptime or desire required to be an active routing node. As a result, these
mobile nodes (which typically use light clients to connect to the Bitcoin p2p
network), instead may have purely unadvertised channels.
An unadvertised channel isn’t part of the known public channel graph, but can still be used to send/receive payments. An astute reader may now be wondering how a channel which isn’t part of the public channel graph is able to receive payments. The solution to this problem is a set of "path finding helpers" that we call "routing hints. As we’ll see in Chapter XX on the presentation/payment layer, invoices created by nodes with unadvertised channels will include auxiliary information to help the sender route to them assuming the no has at least a single channel with an existing public routing node.
Due to the existence of unadvertised channels, the true size of the channel graph (both the public and private components) is unknown. In addition, any snapshot of the channel graph that doesn’t come directly from one’s own node (via a Block Explorer or the like) is to be considered non-canonical as updates to the graph are communicated using a system that only is able to achieve an eventually consistent view of the channel graph.
As mentioned earlier, the channel graph is authenticated due to its usage of
public key cryptography, as well as the Bitcoin blockchain as a spam prevention
system. In order to have a node accept a new channel_announcement, the
advertise must prove that the channel actually exists in the Bitcoin
blockchain. This proof system adds an upfront cost to adding a new entry to the
channel graph (the on-chain fees on must pay to create the UTXO of the
channel). As a result, we mitigate spam and ensure that another node on the
network can’t costless fill up the disk of an honest node with bogus channels.
Given that we need to construct a proof of the existence of a channel, a
natural question that arises is: how to we "point to" or reference a given
channel for the verifier? Given that a channel MUST be a UTXO, an initial
thought might be to first attempt to just advertise the full outpoint
(txid:index) of the channel. Given the outpoint of a UTXO is globally unique
one confirmed in the chain, this sounds like a good idea, however it has one
fatal flow: the verifier must maintain a full copy of the UTXO set in order to
verify channels. This works fine for full-node, but light clients which rely on
primarily PoW verification don’t typically maintain a full UTXO set. As we want
to ensure we can support mobile nodes in the Lightning Network, we’re forced to
find another solution.
What if rather than referencing a channel by its UTXO, we reference it based on
its "location" in the chain? In order to do this, we’ll need a scheme that
allows us to "index" into a given block, then a transaction within that block,
and finally a specific output created by that transaction. Such an identifier
is described in BOLT 7 and is referred to as a: short channel ID, or scid.
The scid is used both in channel_announcement (and channel_update) as
well as within the onion encrypted routing packet included within HTLCs as we
learned in Chapter XX.
Based on the information above, we have 3 piece of information we need to encode in order to uniquely reference a given channel. As we want to very compact representation, we’ll attempt to encode the information into a single integer using existing known bit packing techniques. Our integer format of choice is an unsigned 64-bit integer, which is comprised of 8 logical bytes.
First, the block height. Using 3 bytes (24-bits) we can encode 16777216 blocks, which is more than double the number of blocks that are attached to the current mainnet Bitcoin blockchain. That leaves 5 bytes left for us to encode the transaction index and the output index respectively. We’ll then use the next 3 bytes to encode the transaction index within a block. This is more than enough given that it’s only possible to fix tens of thousands of transactions in a block at current block sizes. This leaves 2 bytes left for us to encode the output index of the channel within the transaction.
Our final scid format resembles:
block_height (3 bytes) || transaction_index (3 bytes) || output_index (2 byes)Using bit packing techniques, we first encode the most significant 3 bytes as the block height, the next 3 bytes as the transaction index, and the least significant 2 bytes as the output index of that creates the channel UTXO.
A short channel ID can be represented as a single integer
(695313561322258433) or as a more human friendly string: 632384x1568x1.
Here we see the channel was mined in block 632384, was the 1568 th
transaction in the block, with the channel output being found as the second
(UTXOs are zero-indexed) output produced by the transaction.
Now that we’re able to succinctly defence a given channel in the chain, we can
now examine the full structure of the channel_announcement message, as well
as how to verify the proof-of-existence included within the message.
A channel announcement primarily communicates two aspects:
-
A proof that a channel exists between Node A and Node B with both nodes controlling the mulit-sig keys in the refracted channel output
-
The set of capabilities of the channel (what types of HTLCs can it route, etc)
When describing the proof, we’ll typically refer to node 1 and node 2. Out
of the two nodes that a channel connects, the "first" node is the node that has
a "lower" public key encoding when we compare the public key of the two nodes
in compressed format hex-encoded in lexicographical order. Correspondingly, in
addition to a node public key on the network, each node should also control a
public key within the Bitcoin blockchain.
Similar to the node_announcement message, all included signatures of the
channel_announcement message should be signed/verified against the raw
encoding of the message (minus the header) that follows after the final
signature (as it isn’t possible for a signature to sign itself..)
With that said, a channel_announcement message (the edge descriptor in the
channel graph) has the following attributes:
-
node_signature_1: The signature of the first node over the message digest. -
node_signature_2: The signature of the second node over the message digest. -
bitcoin_signature_1: The signature of the multi-sig key (in the funding output) of the first node over the message digest. -
bitcoin_signature_2: The signature of the multi-sig key (in the funding output) of the second node over the message digest. -
features: A feature bitvector that describes the set of protocol level features supported by this channel. -
chain_hash: A 32 byte hash which is typically the genesis block hash of the chain the channel was opened within. -
short_channel_id: Thescidthat uniquely locates the given channel within the blockchain. -
node_id_1: The public key of the first node in the network. -
node_id_2: The public key of the second node in the network. -
bitcoin_key_1: The raw multi-sig key for the channel funding output for the first node in the network. -
bitcoin_key_2: The raw multi-sig key for the channel funding output for the second node in the network.
-
what is a gossip protocol?
-
why are they used?
-
what other famous uses of gossip protocols are out there?
-
when does it make sense to use a gossip protocol?
-
what are some use a gossip protocol?
-
why does LN uise
-
questions to ask for gossip rptocol
-
what is being gossiped
-
what is the expected delay bound?
-
how is DoS prevented